1. Field of the Invention
The present invention relates to a reproduction device for decrypting and reproducing encrypted data obtained by a data distribution system, which can secure a copyright relating to copied information.
2. Description of the Background Art
By virtue of the progress in information communication networks and the like such as the Internet in these few years, each user can now easily access network information through individual-oriented terminals employing a cellular phone or the like.
In such information communication, information is transmitted through digital signals. It is now possible to obtain copied music and video information transmitted via the aforementioned information communication network without degradation in the audio quality and picture quality of the copy data, even in the case where an individual user performs the copy.
Thus, there is a possibility of the copyright of the copyright owner being significantly infringed unless some appropriate measures to protect copyrights are taken when any content data subject to copyright protection such as music data and image data is to be transmitted on the information communication network.
However, if copyright protection is given top priority so that distribution of content data through the disseminating digital information communication network is suppressed, the copyright owner who can essentially collect a predetermined copyright royalty for copies of a copyrighted work will also incur some disbenefit.
Instead of the distribution over the digital information communication network described above, distribution may be performed via record mediums storing digital data. In connection with the latter case, music data stored in CDs (compact disks) on the market can be freely copied in principle into magneto-optical disks (e.g., MDs) as long as the duplication is only for the personal use. However, a personal user performing digital recording or the like indirectly pays predetermined amounts in prices of the digital recording device itself and the medium as guaranty moneys to a copyright holder.
However, the music data is digital data, which does not cause deterioration of information when it is copied as digital signals from a CD to an MD. Therefore, for the copyright protection, such structures are employed that the music information cannot be copied as digital data from the recordable MD to another MD.
In view of the above, the public distribution itself of the music data and image data over the digital information communication network is restricted by the public transmission right of the copyright holder, and therefore sufficient measures must be taken for the copyright protection.
For the above case, it is necessary to inhibit unauthorized further duplication of the content data such as music data or image data, which was once distributed to the public over the information communication network.
Such a data distribution system has been proposed that a distribution server holding the encrypted content data distributes the encrypted content data to memory cards attached to terminal devices such as cellular phones via the terminal devices. In this data distribution system, a public encryption key of the memory card, which has been authenticated by an authentication station, and its certificate are sent to the distribution server when requesting the distribution of encrypted content data. After the distribution server determines the reception of the authenticated certificate, the encrypted content data and a license key for decrypting the encrypted content data are sent to the memory card. When distributing the encrypted content data and the license key, the distribution server and the memory card generate a session key, which is different from those generated in other distribution. With the session key thus generated, the public encryption key is encrypted, and the keys are exchanged between the distribution server and the memory card.
Finally, the distribution server sends the license key, which is encrypted with the public encryption key unique to each memory card, and is further encrypted with the session key, as well as the encrypted content data to the memory card. The memory card records the license key and the encrypted content data thus received in a memory.
When the encrypted content data recorded in the memory card is to be reproduced, the memory card is attached to the reproduction terminal. In addition to an ordinary function of the telephone, the reproduction terminal has a dedicated circuit for decrypting the encrypted content data sent from the memory card, and reproducing it for external output. Owing to this circuit, use as the reproduction terminal can be achieved.
As described above, the user of the cellular phone can receive the encrypted content data from the distribution server via the cellular phone, and can reproduce the encrypted content data.
In another manner, encrypted content data is distributed over the internet to personal computers. For distributing the encrypted content data to the personal computers, software installed in the personal computer is used for distributing the encrypted content data.
Music CDs storing music data are very popular, and ripping is performed for obtaining the music data from music CDs. The ripping generates encrypted music data (encrypted content data) from the music data and a license key for decrypting and reproducing the encrypted music data. In this ripping, the content data is encrypted for inhibiting free duplication of the content data obtained by the ripping.
As described above, the music data is distributed as the encrypted content data. It is preferable that the encrypted content data to be distributed is entirely encrypted, as is done in encrypted content data 90 shown in FIG. 37. However, encrypted content data 91, which is prepared by partially encrypting the content data, may be distributed in practical systems. Thus, encrypted regions 911 and non-encrypted regions 912 are mixed in encrypted content data 91 to be distributed.
Encryption and decryption of encrypted content data 90 and 91 are performed by a reproduction terminal 900 shown in FIG. 38.
Reproduction terminal 900 includes a controller 901, a memory card interface 902, a content decrypting circuit 903 and a decoder 904. Controller 901 obtains encrypted content data 91 from memory card 910 via memory card interface 902 for each block, and applies the same to content decrypting circuit 903 via a bus BS6. Memory card interface 902 controls transmission between bus BS6 and memory card 910. When content decrypting circuit 903 receives the encrypted content data, it decrypts the encrypted content data with a license key, and sends it to decoder 904. When plaintext of content data is received, content decrypting circuit 903 outputs the content data to decoder 904. Decoder 904 decodes the content data sent from content decrypting circuit 903, and converts the content data thus decoded from digital signals to analog signals for outputting it to an external output device such as headphones (not shown). Memory card 910 holds encrypted content data 91 divided into a plurality of blocks as well as the license key.
Reproduction terminal 900 reproduces the encrypted content data in accordance with a flowchart of FIG. 39. Referring to FIG. 39, when the operation starts, controller 901 obtains the license key from memory card 910 via memory card interface 902 and bus BS6 (step S1000), and supplies it to content decrypting circuit 903 (step S1001). Controller 901 obtains all the blocks of the encrypted content data from memory card 910 block by block in accordance with the order of reproduction, and supplies them to content decrypting circuit 903. Thereafter, controller 901 determines whether all the blocks forming the encrypted content data are completely obtained from memory card 910 or not (step S1002). If the obtaining of all the blocks has ended, the reproduction operation ends (step S1006). When it is determined in step S1002 that the obtaining of all the blocks has not ended, controller 901 reads out one block from memory card 910 via memory card interface 902 (step S1003), and outputs the block thus read to content decrypting circuit 903 via bus BS6 (step S1004). Content decrypting circuit 903 makes determination on the respective blocks forming the encrypted content data thus supplied in accordance with the order of supply, and more specifically determines whether each block is encrypted or not. If encrypted, the encrypted content data is reproduced by decrypting it with the license key supplied in step S1001. If not encrypted, content decrypting circuit 903 reproduces it as it is. Content decrypting circuit 903 sends a data request to controller 901 so that the following blocks may be supplied thereto in accordance with the timing allowing continuous reproduction.
Controller 901 determines whether data request from content decrypting circuit 903 is present or not (step S1005), and repeats this determining operation until the data request is issued. When content decrypting circuit 903 issues the data request, the operation moves to step S1002, and steps S1002–S1005 are repeated until the end of reproduction of encrypted content data. In this manner, reproduction terminal 900 in the prior art obtains the encrypted content data a block from memory card 910 and reproduces it.
However, the method of reproducing the encrypted content data by the conventional reproduction terminal suffers from such a problem that even the non-encrypted content data formed of only the non-encrypted blocks can be reproduced, and the user can reproduce the content data, which is prepared by free duplication and/or processing without taking any measures for copyright protection. This means the free reproduction of original music data, which is not encrypted. When the original music data in the music CD or the like is freely duplicated and taken into another medium, device or the like, this infringes the right of the copyright holder.
However, duplication for reasonable use by the user must be appropriately allowed, and it is necessary to provide a reproduction device for reproducing only the data, which is duplicated under predetermined rules securing the rights of the copyright holders. Likewise, it is necessary to allow reproduction of the music data, which is prepared under the predetermined rules, and is electronically distributed. In view of complimentary or promotional purposes or the like, it is desired to allows test-listen of a portion, which is formed of the continuous non-encrypted blocks, of the music data prepared based on the above rules before obtaining the license key and thus before paying a fee.